PROJECT SUMMARY The proposed project studies the fate and transport of Superfund-related organic contaminants and the processes controlling their mobility, persistence, distribution, and paths toward potential exposures and/or remediation zones in karst groundwater systems. The project's specific aims are directed at characterizing fate and transport processes and concentration distributions of contaminants in karst groundwater systems typified by variable conduit and/or diffusion dominated flow, as those found in northern Puerto Rico. This region is the focal area of PROTECT's work to study exposure to Superfund hazardous chemicals and their potential contribution to high rates of preterm birth in Puerto Rico, which are the highest among U.S. jurisdictions, second second only to Malawi globally. The project focuses on chlorinated volatile organic compounds (CVOCs) and phthalates as model contaminants because they are ubiquitous and have been shown to have potential health impacts. The research will build on the physical, data, and collaborative research infrastructure developed by the investigators during the first three years of the project. Karst groundwater systems, which provide over 40% of the groundwater used for drinking in the U.S., develop in soluble rocks, such as limestone and dolomites. Flow in these systems may occur through fractures, conduits, and the rock matrix. In such systems, conduits can concentrate water and contaminants from direct sources and/or diffuse flow and convey them rapidly to potential-exposure discharge points such as springs. They can also convey contaminants to trapping diffuse-flow zones, which can result in long-term storage and subsequent release of contaminants. Developing the ability to assess and predict contaminant transport and potential exposure to contaminants in these type of aquifers is essential to understanding and preventing health effects stemming from contaminants in the groundwater. This project will characterize and quantify the factors affecting fate and transport of contaminants in karst systems. Using experimental data and field measurements, spatiotemporal contaminant distributions and transport properties will be characterized, quantified and statistically modeled. Fundamental knowledge developed from hydraulic and transport experiments in laboratory-scale models will be integrated into field- scale measurements and tracer tests through the use of geostatistical methods. At the field scale, contaminant concentrations in groundwater wells and springs in the karst system of northern Puerto Rico will be measured during wet and dry seasons. Field-scale models will be populated with historical contamination, water quality, and hydrogeologic data from the karst groundwater of northern Puerto Rico, and used to describe spatial and temporal changes in contaminant distribution, providing the ability to predict potential dynamic exposure to contaminants in karst groundwater systems and establish strategies to protect public health.